UnityWebRequestを使って変数でPOSTする

Step１：request body -> GetContext()でContextを取得する
Step２: response body -> SetContext()Contextをセットする

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Networking;
using System;


namespace UnityPostTest
{
    public class TestAPIManager : MonoBehaviour
    {
        [SerializeField, Header("入力欄")] TMP_InputField m_InputField = default;
        [SerializeField, Header("レスポンス")] TextMeshProUGUI m_ResponseText = default;
        

        public class Item
        {
            public string testResponse;
            public Item(string testResponse)
            {
                this.Response = Response;
            }

            public override string ToString()
            {
                return string.Format("{0}", Response);
            }

        }

        private string m_testContext;
        private const string baseUrl = "XXXXXXXX";
        private const string url = "/api/v1/test";
        
        //Contextをセット
        public void SetContext(string testContext)
        {
            m_testContext = testContext;
        }
        
        //Contextを取得
        public string GetContext()
        {
            if (string.IsNullOrWhiteSpace(m_testContext))
            {
                m_testContext = "";
            }

            return m_testContext;
        }

        //コルーチンを呼び出す
        public void OnClick(){
            Debug.Log("Sending Post Request");
            StartCoroutine(Post((result) => {
                print("Result from Coroutine:" + result);
            }));
        }

        public IEnumerator Post(Action<string> result)
        {

            string targetUrl = baseUrl + url;
            
            //request body
            WWWForm form = new WWWForm();
            form.AddField("test", m_InputField.text.ToString());
            form.AddField("testContext", GetContext());

            using(UnityWebRequest request = UnityWebRequest.Post(targetUrl, form)){
                request.SetRequestHeader("AUTHORIZATION", "XXXXXXX");
                request.downloadHandler = (DownloadHandler)new DownloadHandlerBuffer();

                // APIリクエストが返ってくるのを待つ
                yield return request.SendWebRequest();
                    
                //エラーのチェック
                if (request.result != UnityWebRequest.Result.Success) {
                    result(request.error);
                }
                else {
                    Debug.Log("Form upload complete!");
                    var item = JsonUtility.FromJson<Item>(request.downloadHandler.text);
                    m_ResponseText.text = item.Response.ToString();
                    //Contextをセットする
                    SetContext(item.Context.ToString());
                    result(request.downloadHandler.text);
                }
            }
        }
    }
}